From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0A342C10F14 for ; Thu, 3 Oct 2019 16:47:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0C8420865 for ; Thu, 3 Oct 2019 16:47:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570121258; bh=9SO459Tx95hQLcr6M3fZdhK5p3dMn/Dz2ldcdyi20Qc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=fHw6+sdLlOuri7NMB3UdNwBSiD/8MD+pds/XIhwDeUZkxsqvHcimNhpfW7sb6MeAN B5GYz2HJ3jZmpSx3z9CjHU35j5v2khCiUp+uWzM/UCasfZe+5O5gWu6eGkmZJV8GYB icnySVG4YkdBRAGJ0BctZFn4q1y5dgReV2SRCjJM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405298AbfJCQrh (ORCPT ); Thu, 3 Oct 2019 12:47:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:32940 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405202AbfJCQre (ORCPT ); Thu, 3 Oct 2019 12:47:34 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 856E12086A; Thu, 3 Oct 2019 16:47:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570121254; bh=9SO459Tx95hQLcr6M3fZdhK5p3dMn/Dz2ldcdyi20Qc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=md9cV8CkeabwpBgC7nspO4ST69xmdZgBAydKC9Ns1hrZVuiFnca8A2oxhfdyKEECL W9KHZafr2n6DGUv/wJudWRvDA5SkYWWIupJCRMZN2QZkHfofo+9BHF56FWBxekWshP mNK7WHWOEDMkgWAsCEEDGNCQjDiaujLuu9MaEv+s= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Dumazet , Jinyu Qi , Joerg Roedel , Robin Murphy , Sasha Levin Subject: [PATCH 5.3 184/344] iommu/iova: Avoid false sharing on fq_timer_on Date: Thu, 3 Oct 2019 17:52:29 +0200 Message-Id: <20191003154558.358824001@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191003154540.062170222@linuxfoundation.org> References: <20191003154540.062170222@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Eric Dumazet [ Upstream commit 0d87308cca2c124f9bce02383f1d9632c9be89c4 ] In commit 14bd9a607f90 ("iommu/iova: Separate atomic variables to improve performance") Jinyu Qi identified that the atomic_cmpxchg() in queue_iova() was causing a performance loss and moved critical fields so that the false sharing would not impact them. However, avoiding the false sharing in the first place seems easy. We should attempt the atomic_cmpxchg() no more than 100 times per second. Adding an atomic_read() will keep the cache line mostly shared. This false sharing came with commit 9a005a800ae8 ("iommu/iova: Add flush timer"). Signed-off-by: Eric Dumazet Fixes: 9a005a800ae8 ('iommu/iova: Add flush timer') Cc: Jinyu Qi Cc: Joerg Roedel Acked-by: Robin Murphy Signed-off-by: Joerg Roedel Signed-off-by: Sasha Levin --- drivers/iommu/iova.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index 3e1a8a6755723..41c605b0058f9 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -577,7 +577,9 @@ void queue_iova(struct iova_domain *iovad, spin_unlock_irqrestore(&fq->lock, flags); - if (atomic_cmpxchg(&iovad->fq_timer_on, 0, 1) == 0) + /* Avoid false sharing as much as possible. */ + if (!atomic_read(&iovad->fq_timer_on) && + !atomic_cmpxchg(&iovad->fq_timer_on, 0, 1)) mod_timer(&iovad->fq_timer, jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT)); } -- 2.20.1